1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for transmitting acknowledgement (ACK)/not-acknowledgement (NACK) indicating a reception confirmation in a carrier aggregation system.
2. Related Art
Long term evolution (LTE) based on 3rd generation partnership project (3GPP) technical specification (TS) release 8 is a promising next-generation mobile communication standard.
Although a carrier having various bandwidths is provided in LTE, it is premised that communication is performed basically using one carrier.
Meanwhile, 3GPP LTE-advanced (A) which is an evolution of 3GPP LTE is under development. A carrier aggregation (CA) is a technique employed in the 3GPP LTE-A.
The CA uses a plurality of component carriers (CCs). The CC is defined with a center frequency and a bandwidth. One downlink (DL) CC or a pair of an uplink (UL) CC and a DL CC corresponds to one cell. When a user equipment receives a service by using a plurality of DL CCs, it can be said that the user equipment receives the service from a plurality of serving cells.
It is premised that the conventional carrier aggregation system aggregates cells which operate with FDD or aggregates cells which use the same UL-DL configuration while operating with TDD.
However, a future wireless communication system considers a case of aggregating a cell operating with FDD and a cell operating with TDD or a case of aggregating cells operating with TDD when each cell uses a different UL-DL configuration.
As such, in case of aggregating cells to which different configurations are applied, ACK/NACK may not be effectively transmitted when using a hybrid automatic repeat request (HARQ) ACK/NACK transmission method and timing in the conventional FDD or FDD.